Directional drilling involves controlling the direction of a wellbore as it is being drilled. It is often necessary to adjust the direction of the wellbore frequently while directional drilling, either to accommodate a planned change in direction or to compensate for unintended and unwanted deflection of the wellbore.
Directional drilling typically utilizes a combination of three basic techniques, each of which presents its own special features. First, the entire drill string may be rotated from the surface, which in turn rotates a drilling bit connected to the end of the drill string. This technique, sometimes called “rotary drilling”, is commonly used in non-directional drilling and in directional drilling where no change in direction during the drilling process is required or intended. Second, the drill bit may be rotated by a downhole motor that is powered, for example, by the circulation of fluid supplied from the surface. This technique, sometimes called “sliding drilling,” is typically used in directional drilling to effect a change in direction of a wellbore, such as in the building of an angle of deflection, and almost always involves the use of specialized equipment in addition to the downhole drilling motor. Third, rotation of the drill string may be superimposed upon rotation of the drilling bit by the downhole motor.
In the drill string, the bottom-hole assembly is the lower portion of the drill string consisting of the bit, the bit sub, a drilling motor, drill collars, directional drilling equipment and various measurement sensors. Typically, drilling stabilizers are incorporated in the drill string in directional drilling. The primary purpose of using stabilizers in the bottom-hole assembly is to stabilize the bottom-hole assembly and the drilling bit that is attached to the distal end of the bottom-hole assembly, so that it rotates properly on its axis. When a bottom-hole assembly is properly stabilized, the weight applied to the drilling bit can be optimized.
A secondary purpose of using stabilizers in the bottom-hole assembly is to assist in steering the drill string so that the direction of the wellbore can be controlled. For example, properly positioned stabilizers can assist either in increasing or decreasing the deflection angle of the wellbore either by supporting the drill string near the drilling bit or by not supporting the drill string near the drilling bit.
Conventional stabilizers can be divided into two broad categories. The first category includes rotating blade stabilizers which are incorporated into the drill string and either rotate or slide with the drill string. The second category includes non-rotating sleeve stabilizers which typically comprise a ribbed sleeve rotatable mounted on a mandrel so that, during drilling operations, the sleeve does not rotate while the mandrel rotates or slides with the drill string. Some stabilizers have blades that are of a fixed gauge and other stabilizers, typically referred to as adjustable gauge stabilizers, have the ability to adjust the gauge during the drilling process.
Although a stabilizer having straight blades is suitable for slide drilling, straight blades tend to cause shock and vibration in the bottom-hole assembly when rotary drilling. Wrapped blades can limit vibration in the bottom-hole assembly when the drill string is rotated. However, during slide drilling, wrapped blades tend to “corkscrew” themselves into a tight wellbore and get stuck. This invention seeks to provide an adjustable gauge stabilizer that is beneficial for slide drilling, while providing more circumferential contact with the borehole wall. This contact will prevent detrimental downhole shocks and vibrations when the drill string is rotated.